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Junctions were formed in thin SiGe/strained Si substrates with a thickness of 250-350 nm to assess the effect of different buffer layer parameters (bandgap, dislocations, thickness) on the junction leakage density that can be expected in MOSFET devices. The implantations used are standard well, channel and Highly Doped Drain (HDD) implants. Both p+/n and n+/p junctions were evaluated. The total thickness of the buffer layers was varied to compare the effect of different structural layers on the diode leakage. This investigation shows that the effect of an increased defect density is dominant at room temperature for the strained Si samples, resulting in 4-5 orders of magnitude increase in leakage. However, there is a different gradation in leakage dependence for thick and thin buffer layers, especially at higher temperatures.

Results are presented of a study on the mechanical stress dependence of the resistance of polycrystalline silicon (Poly-Si) films, doped with different atomic species. Two types of Poly-Si film implanted with boron and phosphorus ions were studied, namely, B-doped films of 400 nm and P-doped layers of 250 nm thickness, which were deposited by LPCVD at 620 °C on thermally oxidized silicon wafers. Film doping was done by ion implantation at 50 keV, with a dose of boron and phosphorus of 2 × 1014 and 5.3 × 1014 cm−2, respectively. The Poly-Si films were annealed in a H2 ambient at 1000 °C for 20 min to activate the implanted atoms. A controlled amount of external stress was applied to the silicon wafers in order to study the impact on the electrical performance of the implanted Poly-Si resistors. The resistance of the B-doped Poly-Si films is shown to increase by the mechanical stress, while the resistance of the P-implanted Poly-Si films remained unchanged. It is concluded that this difference is related to the structural differences between Poly-Si films implanted with boron and phosphorus, respectively.

The recombination activity of oxygen precipitation related lattice defects in p- and n-type silicon is studied with photoluminescence (PL) and microwave absorption (MWA) techniques. A direct correlation is observed between the amount of precipitated oxygen and the extended defect density on one hand and the minority carrier lifetime and PL activity on the other hand. The PL analyses show as dominant features in the spectra the Dl and D2 lines. The relative amplitude of the D-lines in the different samples is investigated as a function of the oxygen content, defect density and excitation level. The results are correlated with those of complementary techniques and are interrelated on the basis of Shockley-Read-Hall (SRH) theory.

The results are presented of a fundamental study of electrically active damage introduced in silicon diodes by irradiation with the fission products resulting from the decay of a 252Cf source and with high energy protons. The influence of the oxygen content of the silicon substrate and the irradiation type on the damage formation is investigated using deep level transient spectroscopy. A radiation hardening effect by interstitial oxygen is observed. Bom types of irradiation create the same dominant defect levels but with different relative densities. The identification of the induced deep levels are confirmed by isochronal annealing results.

Results are presented of a study on the degradation of the electrical performance of Fe contaminated n+p Si diodes, subjected to a 220-MeV carbon irradiation. The reverse current of the diodes increases after irradiation, while the capacitance and hence the doping concentration decreases. The areal and peripheral components of the leakage current are extracted from diodes with different area to perimeter ratios. Both the generation and the recombination lifetime calculated from I/V and C/V characteristics also decrease. The deep levels in the Si substrate induced by the irradiation are mainly responsible for the degradation of the diode performance. The radiation damage is also studied for 1 -MeV electrons and 1 -MeV fast neutrons. The performance degradation for carbon irradiation is three orders of magnitude larger than that for electron irradiation. The differences in the radiation damage are explained by the differences in the number of knock-on atoms and the nonionizing energy loss (NIEL), which is attributed to the difference of mass and the possibility of nuclear collision with target Si atoms

Results are presented of a study on the degradation of the electrical and optical performance of n+p Si avalanche photodiodes, subjected to 1-MeV fast neutrons and to a 220-MeV carbon irradiation. The dark current increases after irradiation, while the photo current decreases. Two dominant hole capture levels, which are responsible for the degradation of performance, are after irradiation observed by DLTS (Deep Level Transient Spectroscopy). The degradation caused by neutron irradiation is smaller than that for carbon irradiation. The differences in the radiation damage are explained by the differences in the number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the device performance by isochronal annealing is also reported.

Results are presented for the first time of a study on the degradation of the electrical performance of MOSFET's processed on SIMOX substrates and subjected to a 220-MeV carbon irradiation. For the n-MOSFETs an unstable increase of the drain current in linear operation is found, while for the p-MOSFETs, a drastic reduction is observed, both in linear operation and in saturation. The radiation damage is also compared to the results for 1-MeV electrons, 1-MeV fast neutrons and 20-MeV alpha rays. The differences in the damage coefficients are explained by the differences in the number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the device performance by isochronal annealing is also reported.

The degradation of the electrical performance of strained Si1-xGex epitaxial diodes by 220-MeV carbon particles is reported and compared with the effect of 20-MeV alpha rays and 20-MeV protons. The macroscopic damage is studied in a broad fluence range and for different Ge contents, ranging from 8 to 16 %. It is shown that the radiation damage of carbon irradiated diodes is about one order of magnitude larger than that for alpha ray irradiation, which can be explained by considering the difference of the nonionizing energy loss (NIEL). It is observed that the reverse current at a fixed bias increases with increasing fluence, while the rate of increase decreases with increasing fluence and/or Ge content. The fact that a close to square root dependence exists between the boron deactivation in the diode depletion region, derived from capacitance-voltage measurements and the reverse current increase suggests that the device degradation is dominated by radiation induced deep levels associated with interstitial boron complexes.

Results are presented of a study on the performance degradation and the induced lattice defects of In0.53Ga0.47As p-i-n photodiodes, subjected to 220-MeV carbon particles. The effects on both the dark current and the photo-current are investigated as a function of the carbon fluence and correlated with DLTS results. The device degradation is compared with the one observed after exposure to 1-MeV electrons, 1-MeV fast neutrons and 20-MeV alpha rays, respectively. The differences in damage coefficients will be explained in view of the calculated number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the diode performance and of the induced deep levels by isochronal annealing is also reported.

The electrical performance of junctions in SiGe Strain Relaxed Buffers (SRB's) with a strained Si top layer is investigated. Most of the SRB's grown in this experiment use a thin C-doped SiGe layer, which allows to fabricate thin (∼250nm) SRB's with a high relaxation degree. The effects of Threading Dislocation Density (TDD) and C-rich layer depth on the electrical behaviour of n+/p and p+/n junctions are studied. The C atoms in the junction's Space Charge Region (SCR) give rise to defects and induce a noticeable increase in the leakage. The effect of the TDD on the leakage in n+/p junctions is linear over the complete voltage range applied, while for p+/n junctions, only a small effect on leakage is measured at V=1V reverse for TDD's below 1×107cm-2. For low reverse voltages, the current varies more linearly with TDD.

A rather large amount of shallow donors is created in p-type Czochralski silicon (Cz Si) wafers after a hydrogen plasma exposure at ∼270 °C (substrate temperature) and a subsequent annealing in the temperature range of 350-450 °C. This two-step process has been used for the fabrication p-n junction diodes at low temperatures. Current-voltage characteristics show that the breakdown voltages of these diodes are higher than 100 V. The diode leakage is found to be improved after slow ramp annealing at temperatures up to 250 °C. Deep level transient spectroscopy measurements reveal that the oxygen related thermal donor is not the dominant doping species as expected before.

Thermal donor formation was studied in oxygen enriched high resistive float zone silicon (FZ Si:Oi). Such substrates are used e.g. for radiation hard detectors or high voltage devices. RF Plasma hydrogenation (110 MHz, 50 W) was carried out at 250°C for 1 hour. Subsequent annealing was done at 450°C/air for up to 50 h. The plasma treated and annealed FZ Si:Oi samples were analyzed by spreading resistance probe, capacitance-voltage and DLTS measurements. It is shown that a rapid formation of donors can be observed in oxidized FZ Si:Oi, but in a somewhat different way than in Czochralski (Cz) Si. While in Cz Si the hydrogen enhanced formation of ‘old’ thermal double donors occurs under the applied processes, in FZ Si:Oi most probably the formation of new hydrogen related shallow donors can be assumed.

High mobility channel materials and new device structures will be needed to meet the power and performance specifications in future technology nodes. Therefore, the use of Ge and III/V materials and novel devices such as heterojunction TunnelFET’s is investigated for future CMOS applications. High-performance CMOS can be obtained by combining Ge pMOS devices with nMOS devices made on III/V compounds such as InGaAs. In all cases the key challenge is the electrical passivation of the interface between the high-k dielectric and the alternative channel materials.
Recent studies have demonstrated good electrical properties of the GeO2/Ge interface. Since the GeO2 layer is very hygroscopic, full in-situ processing of GeO2 formation and high-k deposition must be performed or other methods must be employed to stabilize the GeO2 layer. One of the most successful passivation techniques for Ge MOS gate stacks is a thin, epitaxial layer of Si. A lot of attention went into better understanding of this passivation and the effects of its optimization on various device characteristics. It was found that mobility and Vt trends in both pMOS and nMOS transistors can be explained based on defects located at the Si/SiO2 interface.
Unfortunately, III-V/oxide interfaces are not quite as robust and most interfaces present rather high densities of interface states. Although, considerable improvements have been realized in the reduction of the interface state density, further developments are required to obtain high performance MOS devices. To this purpose various passivation methods were critically evaluated. Simulations using Density Functional Theory reveal the possibility of using a thin amorphous layer made of GeOX to obtain an electrically unpinned gap. The major challenge resides in the control of the c-Ge thickness and the oxidation of this layer to avoid the diffusion of oxygen atoms at the Ge/GaAs(001) interface. Promising results are obtained by optimizing the surface preparation, high-k deposition and annealing cycle on In0.53Ga0.47As-Al2O3 interfaces. Self-aligned inversion channel n-MOSFETs fabricated on p-type In0.53Ga0.47As demonstrate inversion-mode operation with high drive current and a peak electron mobility of 3000 cm2/Vs.
Since ultimately the major showstopper on the scaling roadmap is not device speed, but rather power density, the introduction of these advanced materials will have to go together with the introduction of new device concepts. Novel structures such as heterojunction TunnelFET’s can fully exploit the properties of these new materials and provide superior performance at lower power consumption by virtue of their improved subthreshold behaviour. Vertical surround gate devices produced from nanowires allow the introduction of a wide range of materials on Si. This illustrates the possibilities that are created by the combination of new materials and devices to allow scaling of nanoelectronics beyond the Si roadmap.

Electrical properties of the shallow thermal donors (TDs) in n-type
CZ-Si diodes by the electron irradiation were investigated. After
the electron irradiation, carrier concentration was decreased. From
deep level transient spectroscopy (DLTS) measurements, some peaks
related to TDs and vacancy-oxygen complexes were observed for the
irradiated samples. The peak related to V-O and/or A-center at
EC-0.18 eV increased with the electron fluence. To compare that,
the level of EC-0.09 eV related to TDs was independent of
electron fluence. In addition to that, reverse current of the diodes
was increased with increasing irradiated electron fluence.

Results are presented of a study on the mechanical stress dependence of the resistance of polycrystalline silicon (Poly-Si) films doped with different atomic species. Two types of Poly-Si film implanted with boron and phosphorus ions were studied, namely, B-doped films of 400 nm and P-doped films of 250 nm thickness, which were deposited by low-pressure chemical vapor deposition at 620 °C on thermally oxidized silicon wafers. The film doping was done by ion implantation at 50 keV, with a dose of boron and phosphorus of 2 × 1014 and 5.3 × 1014 cm−2, respectively. The Poly-Si films were annealed in a N2 ambient at 1000 °C for 20 min to activate the implanted atoms. A controlled amount of external stress was applied to the silicon wafers to study the impact on the electrical performance of the implanted Poly-Si resistors. The resistance of the B-doped Poly-Si films is shown to increase by the mechanical stress, while the resistance of the P-implanted Poly-Si films remained unchanged. It is concluded that this difference is related to the structural differences between Poly-Si films implanted with boron and phosphorus, respectively.

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